The present invention relates in general to telecommunication systems, and is particularly directed to a delimiter code insertion mechanism for achieving byte alignment during remote provisioning and interrogation of a network element interface (NEI) device, such as a digital data services termination (DDST) unit, by a test system controller. To establish a virtual communication path, the test system controller transmits a link establishment code sequence that contains a prescribed select code/byte, which is exclusive of those codes currently employed to represent functional operations to be executed by one or more channel units, so that the destination DDST is not prevented from receiving the link establishment code sequence. In particular, the replacement select code is defined so as to cause the link establishment message to be ignored by intermediate data port units, so that the link establishment message is conveyed all the way to the destination DDST.
As described in the U.S. Patents to S. Killian et al, U.S. Pat. Nos. 5,390,179 and 5,574,723, entitled: xe2x80x9cRemote Provisioning of Telephone Channel Unit Using Inband Digital Code Sequences Transmitted Over Tandem Link,xe2x80x9d assigned to the assignee of the present application and the disclosures of which are incorporated herein, one of the reasons that the telephone companies have been slow to convert to digital signalling subsystems, and incorporate digital communication schemes into their well established copper wire networks, has been the fact that a significant part (if not all) of their established telephone networks employ analog signalling equipment.
To be accepted by the telephone industry, digital products must not only be cost effective substitutes, but must be compatible with any remaining analog equipment. In order to satisfy these requirements, the assignee of the present application has offered and continues to supply various types of digital data port or channel units, that not only facilitate the replacement of conventional analog equipment with digital devices, that allow signalling, voice and data communications to be extended over a tandem communication link and a local loop to a customer premises, but do so without totally preempting the conventional use of analog signalling for maintenance and testing.
With these objectives in mind, the above-referenced Killian et al Patents describe a digitally implemented scheme that allows any channel unit tandemly distributed along a communication path to be selectively remotely accessed and provisioned by a test system controller. This remote access and provisioning mechanism involves a modification of their communication control software, and a modified set of in-band digital code sequences that are customarily used to establish a latching loopback condition.
To initiate a communication session with a selected channel unit, the test system controller transmits a xe2x80x98control link establishment code sequencexe2x80x99 comprised of predefined digital code bytes that are repeatedly transmitted along the link. The format of the control link establishment sequence is such that as it is forwarded along the link, any tandem channel unit or units intermediate the test system controller and the destination channel unit will transition to a transparent state. This communication transparency of the intermediate units allows a control link establishment code set within the overall control link establishment sequence, which will enable the destination channel unit to receive and respond to command messages from the test system controller, to propagate down the link to the destination channel unit, so that only the destination channel unit will be able transition to an interrogation, response mode.
Once it has acknowledged receipt of the control link establishment code setxe2x80x94indicating that a virtual point-to-point, command-response control link has been established with the test system controllerxe2x80x94the selected or destination channel unit transitions to a command-response mode. During this command-response mode, any intermediate channel unit remain transparent, so that command and response messages propagate unmodified between the test unit controller and the destination channel unit.
A command message may contain information for defining the operational configuration of the selected channel unit. It may also be used to read the operational configuration or status of the selected channel unit, or it may contain supervisory control information for directing the selected channel unit to conform with a prescribed operational condition. It has been found that where the channel unit to be accessed is a network element interface (NEI) such as a digital data services termination (DDST) that terminates a local DDS loop, there is a potential problem in determining proper byte alignment for the remote provisioning protocol employed for various violation mode rates, including, for example, 56 Kbps (56K), 38.4 Kbps, 19.2 Kbps, 9.6 Kbps, 4.8 Kbps and 2.4 Kbps.
In accordance with the present invention, this potential problem is successfully addressed by defining the remote provisioning protocol to include a delimiter byte inserted between successive ones of repeated bytes that make up command and response code sequences between the test system controller and the loop terminating NEI device. Similar to the scheme described in the above-referenced Killian patents, the control link establishment sequence comprises a prescribed set of digital code bytes, including those for a latching loopback condition of a channel unit. The control link establishment code sequence according to the present invention is the code or byte set: a transition in progress (TIP) code; a prescribed loopback select code, termed simply a select code (SC), which is exclusive of those codes currently employed to represent functional operations that are executable by a channel unit; a loopback enable (LBE) code, and a far end voice (FEV) code.
Also, unlike the code sequence described in the Killian patents, there is no code conversion by an intervening channel unit, and the transparent mode is not used. Instead, when an intervening channel unit sees the select code (SC), it simply ignores the message; this ensures that the link establishment message is conveyed all the way to the destination DDST.
When the NEI/DDST detects the xe2x80x98link establishmentxe2x80x99 code sequence, it transitions to the command-response mode, so that an xe2x80x98active sessionxe2x80x99 of exchanging messages with the test system controller may be conducted. During this active session, all commandxe2x80x94response messages are formed of the four code set: Start-Of-Message (SOM), Command Type (CT), operational parameter codes (DATA), and End-Of-Message (EOM). In order to provide for byte alignment, each of these respectively different code bytes is repeatedly transmitted a plurality of times, and a xe2x80x98delimiterxe2x80x99 byte is interleaved with or alternates between successively repeated ones of the same code byte. Transmitting the same code byte in an alternating manner with the delimiter byte continues until proper response codes are returned from the NEI device. All response messages from the NEI device are also in the form of code repeats each of which is separated by interleaved delimiter bytes.